The System - An Overview

The safety of flight has been greatly enhanced in recent years by audible warning, or alert, systems which provide the flight crew with early warning of an operational error or aircraft system malfunction.

The objective of the system is to attract the attention of the flight deck crew stating with accuracy the nature and location of a problem.

It has demonstrated over many years that it is effective, highly reliable and also, importantly, not liable to activation when flight conditions are normal. Meeting these objectives has gained the trust of pilots and also saved many lives.

There are two main types of warning systems which are found in most commercial aircraft;

The Two Types of Systems

There are two main types of warning systems which are found in most commercial aircraft;

The Ground Proximity Warning System (GPWS) which was designed to alert pilots to the fact that their aircraft is in danger of flying into the ground.

The Traffic Collision Avoidance System (TCAS) which was devised to prevent or reduce the likelihood of a mid-air collision between two aircraft.

The TCAS monitors the location of other aircraft fitted with the system and sends out an audible alert to warn pilots of any aircraft which could be on a collision course. It is installed in most commercial or business aircraft but is mandatory in aircraft which can carry twenty passengers or more.

Audible Warning Sounds

The audible warning is generally a male voice, with an urgent articulation style, in a distinct American, British or sometimes French accent depending on the type of aircraft and will normally be preceded by a sound such as a bell or horn to get the flight crews full attention.

Despite early research seeming to suggest that male pilots found the female voice more commanding, further reviews carried out since more females began working in the aviation industry, has determined that a computerised female voice is no more or less effective than a male voice.

The audible sounds are usually repeated until the crew take the required action.

GPWS Warnings

Some of the common GPWS warnings and their meaning;

“Pull Up - Sink Rate” Descending to fast

“Too Low –Terrain” Aircraft is getting to close to the ground

“Too Low – Gear” The aircraft is too low to the ground and the undercarriage has not been put into landing position for landing

“Too Low – Flaps” The aircraft is too low to the ground and the wing flaps have not been set for landing

“Pull-Up - Terrain” The ground is approaching to quickly or there is ground ahead that is higher than the aircraft is flying

“Don’t Sink” Excessive height is being lost after take off

“Windshear” Excessive gusts of wind which could affect the aircraft as it comes into land

“Glideslope” Aircraft has drifted from the glideslope when approaching to land

“Increase Climb” Other aircraft will pass just below. Climb immediately at a faster rate.

“Increase Descent” Other aircraft will pass just above. Descend immediately at a faster rate.

“Climb, Climb – Now” Other aircraft which was above, will now pass below. Climb immediately.

“Descend, Descend – Now” Other aircraft which was below, will now pass above. Descend immediately.

“Don’t Climb” Issued instead of “Descend Descend” when the aircraft is at a low height. The aircraft must only descend if the crew can confirm it is safe to do so otherwise they will level off and remain at that height.